The present invention refers to a ball balancing arrangement for a wash drum in a laundry washing machine, in which the wash drum is rotatable about an axis and the arrangement comprises at least one closed annular path being concentrically disposed with respect to the axis, adapted to rotate in synchronism with the wash drum and containing a plurality of moveable ball-shaped balancing bodies which are kept together in groups by a corresponding number of retaining means of a shape so as to keep the ball-shaped balancing bodies in each group out of contact with one another.
A ball balancing arrangement of the kind referred to is used for balancing of the rotating wash drum which supports the laundry. During the finalizing water extraction process the wash drum is driven up into high speed where the imbalance caused by the unevenly distributed laundry may subject the various supporting details of the washing machine to substantial stress.
Among prior art balancing arrangements reference can be made to the one disclosed in the patent publication GB-A-1598399. In this arrangement annular paths are provided at both ends of a wash drum in a laundry washing machine. The paths are partly filled with balls which can move freely in the respective path taking positions such as to counterbalance, during the water extracting process, the imbalance caused by the laundry. A similar arrangement is disclosed in the patent publication U.S. Pat. No. 2,984,094.
In the arrangements described in the publications referred to above the balls are allowed to move freely which means that they are permitted to get into contact with one another. As a result, if a larger group of balls contacting one another are disposed in the lower part of the path, at a later displacement of the balls into positions where balance is achieved, the mutual contact between the balls and the associated friction will cause a delay of the movement so that the desired condition of balance will not fully be achieved. This presents a significant drawback as a compliance as great as possible is desired for the balancing arrangement. In addition, during the setting movement acceleration and retardation of the balls can cause the balls, off and on, to collide with one another disturbing the setting process and also causing undesired noise.
Another solution has been presented which partly meets with the problem of the balls disturbing one another during the setting movement. This solution is disclosed in the patent publication U.S. Pat. No. 3,799,619. Here, the balancing bodies have the shape of elongate weights resting on balls and at the same time being designed to operate as ball retainers. For example, such balancing body may have a curved shape adapted to the annular path and a weight corresponding to say three ordinary balancing balls. Accordingly, in this case the balancing weight has the shape of a small carriage at its ends supported by steel balls. Normally, three such carriages are required for a good balancing to be achieved. The disadvantage of this design is that the ball retainer constitutes the balancing weight and hence that the balls have to support this weight when moving the balancing body into positions where balance is achieved. The inevitable friction losses between the balancing weight and the balls and between the latter and the path will increase. At the same time the advantage is that to a great extent ball collisions are avoided together with the associated delays and noise. An embodiment of the kind referred to is also described in the patent publication WO 96/03541.
The purpose of the invention is to remedy the drawbacks indicated in connection with the prior art balancing arrangements discussed above and to provide an arrangement in which the system is kept which has a plurality of balancing bodies freely moveable but where the bodies, which, contrary to the arrangements according to U.S. Pat. No. 3,799,619 and WO 96/03541, still represent the balancing weight, are retained in groups by ball retainers which are very light and have a low friction with respect to the balls. Accordingly, according to the invention a ball balancing arrangement of the kind referred to above is characterized in that each of the retaining means has a weight which is substantially negligible in comparison to the balancing bodies and in that the surfaces of the retaining means bearing against the balancing bodies have a low friction.
An advantage with the arrangement of the invention in which the balancing weight is divided into a plurality of ball-shaped partial weights which can move by rotating independently of each other in a light-weight ball retainer under low friction is that each partial weight is separately driven by the imbalance force that is present and accordingly that each group of balancing bodies is more compliant, i.e. it can carry out necessary movements faster than in the case where the imbalance weight has the shape of one single body supported by balls. The light-weight ball retainer does not essentially contribute to the balancing weight but has the object only to keep a group of balls together so that they can rotate without touching one another and with no substantial friction against the bearing surfaces of the ball retainer.